Wash fresh rose hips, trim stems and blossom ends, and cut into halves or quarters. Discard damaged hips. If using dried hips, lightly crush them with a mortar and pestle or food processor.
Add rose hips and 6 cups of water to a large saucepan. Bring to a boil, then reduce to a gentle simmer for 20–25 minutes, until softened and liquid has reduced by about half. If using whole hips, mash them gently once softened.
Strain the mixture through a cheesecloth-lined sieve into a bowl. Press the pulp to release liquid, then gather the cloth and squeeze out any remaining juice. Strain twice for smoothness.
Let the strained liquid cool until warm but not hot (about 110–120°F / 43–49°C).
Stir in 3 cups raw honey, adjusting to taste, until fully dissolved. Add vanilla extract here if using.
Pour the syrup into sterilized bottles or jars. Store in the refrigerator for 3–4 weeks, or freeze in small portions for longer storage.